1. Field of the Invention
The present invention relates to a top-coating composition, for a photolithography process, and a process for forming a pattern using the same.
2. Description of the Background Art
Chemical amplification-type DUV photoresists have been used to achieve high sensitivity in minute image formation processes for preparing semiconductor devices. Such photoresists are prepared by blending a photoacid generator and a matrix resin polymer having an acid labile group.
It is believed that when a photoresist (sometimes referred to as “PR”) composition is illuminated by an appropriate light source the photoacid generator generates acid. The resin (i.e., polymer) which is present in the photoresist decomposes or becomes cross-linked when reacted with the generated acid. This change in the resin results in the solubility differences in the developing solution between the exposed portion and the unexposed portion. Thus, by using an appropriate mask, one can form a predetermined pattern using the photoresist composition.
In a lithography process, the image resolution generally depends on the wavelength of the light source, e.g., a shorter wavelength allows a more minute image pattern formation.
Lithography processes employing light sources having a wavelength below 250 nm have been recently investigated. In particular, there have been a lot of interests directed to a polymer containing alicyclic derivatives in its main or branched chain as a suitable photoresist polymer. However, utilizing these alicyclic polymers to a semiconductor fabrication process has many disadvantages. For example, chemical properties of the alicyclic polymer vary. In addition, the generated acid may be neutralized by environmental amine compounds during the time between the exposure and the post exposure baking (i.e., “post exposure delay effect”). As a result, a desired resolution are often not obtained and/or the pattern can be T-shaped (i.e., “T-topping”). One or more of these problems are especially acute when the concentration of environmental amine is over 30 ppb, which in some instances may lead to no pattern formation.
In order to overcome the aforementioned disadvantages, the following methods have been suggested in the prior art:
(1) An annealing method whereby the PR resin is baked over its glass transition temperature (Tg) after the PR is coated [see W. D. Hinsberg, S. A. MacDonald, N. J. Clecak, C. D. Snyder, and H. Ito, Proc. SPIE, 1925, (1993) 43; H. Ito, W. P. England, R. Sooriyakumaran, N. J. Clecak, G. Breyta, W. D. Hinsberg, H. Lee, and D. Y. Yoon, J. Photopolymer Sci. and Technol., 6, (1993) 547; G. Breyta, D. C. Hofer, H. Ito, D. Seeger, K. Petrillo, H. Moritz, and T. Fischer, J. Photopolymer Sci. and Technol., 7, (1994) 449; H. Ito, G. Breyta, D. Hofer, R. Sooriyakumaran, K. Petrillo, and D. Seeger, J. Photopolymer Sci. and Technol., 7, (1994) 433; H. Ito, G. Breyta, R. Sooriyakumaran, and D. Hofer, J. Photopolymer Sci. and Technol., 8, (1995) 505];
(2) Adding an amine compound to the PR [see Y. Kawai, A. Otaka, J. Nakamura, A. Tanaka, and T. Matsuda, J. Photopolymer Sci. and Technol., 8, (1995) 535; S. Saito, N. Kihara, T. Naito, M. Nakase, T. Nakasugi, and Y. Kat. Photopolymer Sci. and Technol., 9, (1996) 677; S. Funato, Y. Kinoshita, T. Kuto, S. Masuda, H. Okazaki, M. Padmanaban, K. J. Przybilla, N. Suehiro, and G. Pawlowski, J. Photopolymer Sci. and Technol., 8, (1995) 543]; and
(3) Adding a top-coating to the upper portion of the PR to protect it against an environmental amine contamination, after the PR coating step and the baking step [see J. Nakamura, H. Ban, Y. Kawai, and A. Tanaka, J. Photopolymer Sci. and Technol., 8, (1995) 555; A. Oikawa, Y. Hatakenaka, Y. Ikeda, Y. Kokubo, S. Miyata, N. Santoh, and N. Abe, J. Photopolymer Sci. and Technol., 8, (1995) 519].
Even using one or more of these techniques it is difficult to form an ultrafine pattern. In addition, the above methods have other disadvantages, such as adding complication or additional steps to a lithography process.